Newsgroups: sci.space.history
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Apollo Vibration testing.....
Date: Sat, 19 Feb 2000 20:04:39 GMT

In article <38ACCE1F.235C1261@rcc.on.ca>,
Cary Martynuik  <cary@rcc.on.ca> wrote:
>...I was wondering what kind
>of vibration testing the CM/SM and, more importantly (due to its
>fragility) the LM were subjected to prior to launch?

I don't know details for Apollo in particular, but vibration testing of
spacecraft is quite routine.  Basically, you hook the thing up to a set of
big high-speed actuators, and shake it for a while and see if anything
comes loose.

>	Also, how exactly was the LM buffered from the walls of the booster
>during launch? Just how tightly was this thing packed in there?

The LM was mounted by its "knees", the ends of its landing-gear supports,
to the upper rim of the fixed part of the LM adapter.  The descent stage
had quite a bit of extra room around the body, because the knees stuck
out somewhat.  The ascent stage's fit was close in places.

Nothing special was done about keeping the LM off the walls, except to
allow some room in between.  (This is quite standard practice:  the
payload has to stay within the "dynamic envelope", which is smaller than
the actual payload shroud to allow for shroud vibration.)

There were some contingency situations where attention was needed.  For
example, the first-stage engines were splayed out slightly, rather than
firing exactly vertically, to bring their thrust lines closer to the
rocket's center of mass.  If a first-stage engine failed, the autopilot
would (in most cases) catch the thrust imbalance and correct it, but with
the original design, the lurch could be violent enough to damage the LM.
Splaying the engines reduced the imbalance and kept the LM loads down.

>	Was there any problems that occurred with any equipment either in the
>CM/SM or LM during any of the Apollo flights (or any flights for that
>matter) that was directly attributed to damage from liftoff violence?

I (don't believe any of the Apollos had any trouble with this.  Apollo 6
had some damage to the LM adapter that was at first thought to be due to
the first-stage Pogo, but it turned out to have a different cause.  The
launch damage to Skylab was from aerodynamic forces, not vibration.

Vibration and acceleration during launch *have* sometimes damaged
payloads.  One of the early Pegasus payloads, ALEXIS, had a solar array
break off on the way up.  (Pegasus at least sometimes flies with a
slow-scan TV camera in the payload shroud, which supplied the proof of
this.)
--
The space program reminds me        |  Henry Spencer   henry@spsystems.net
of a government agency.  -Jim Baen  |      (aka henry@zoo.toronto.edu)